refactor(tags): unify suggestion source — one canonical DB-tag dropdown, drop dead raw/alias machinery (#154)

Every tag suggestion is a canonical DB tag now (tagging-v2 #114: heads + CCIP
score EXISTING concept tags). The pre-heads apparatus for model-predicted tags
that didn't exist in the DB — creates_new_tag / raw_name / via_alias, the
/suggestions/alias endpoint + add_alias_and_accept, AliasPickerDialog, and the
store's aliasAccept/removeAlias — was dead and is removed.

The type-to-add dropdown was TWO row sources (server autocomplete + the image's
ML suggestions) merged with a dedup that dropped the %-bearing suggestion row
when the debounced server hit landed — the operator's "confidence % flickers
then vanishes". Now it's ONE list of DB-tag matches, each annotated with the
model's confidence (join by canonical_tag_id) when the tag was scored for this
image. No dedup, no flicker; picking a suggested tag still records acceptance
via TagPanel.findPending.

Single per-image fetch: score_image now reports above_threshold per row
(computed vs the head's own suggest cut, separate from the inclusion floor), so
the rail makes ONE min=0 request and derives the panel (above_threshold) and the
dropdown (all, text-filtered) client-side — the two /suggestions calls collapse
to one. Manual "Create 'X' as <kind>" (novel typed names) is unchanged; the
alias table + tag-side alias admin + auto-apply alias matching are untouched.

Tests: gate/serializer assertions updated (above_threshold; dropped dead-field
+ alias-endpoint checks); frontend spec seeds via the single load and covers the
byCategory/aboveByCategory split.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CgZP9v2otxVJymiYsnVuMy

backend/app/api/suggestions.py

@@ -11,10 +11,11 @@ suggestions_bp = Blueprint("suggestions", __name__, url_prefix="/api")
 
 @suggestions_bp.route("/images/<int:image_id>/suggestions", methods=["GET"])
 async def get_suggestions(image_id: int):
-    # ?min=<float> overrides the configured per-category thresholds so the typed
-    # tag-input dropdown can surface EVERY stored prediction (min=0), including
-    # low-confidence actions/features, in canonical formatting. Omitted → the
-    # curated above-threshold list the Suggestions panel uses.
+    # ?min=<float> overrides the per-head suggest thresholds for INCLUSION. The
+    # rail sends min=0 in its single per-image fetch to get EVERY head (each row
+    # still carries above_threshold vs its natural cut), then derives the panel
+    # (above_threshold) and the typed dropdown (all, filtered by text) client-side
+    # — no second request. Omitted → only above-threshold rows.
     override = None
     raw_min = request.args.get("min")
     if raw_min is not None:
@@ -36,12 +37,11 @@ async def get_suggestions(image_id: int):
                         "category": s.category,
                         "score": round(s.score, 4),
                         "source": s.source,
-                        "creates_new_tag": s.creates_new_tag,
-                        # raw model key (alias is stored under this) + whether an
-                        # operator alias produced this suggestion — drive the
-                        # modal's "Treat as alias"/"Remove alias" affordances.
-                        "raw_name": s.raw_name,
-                        "via_alias": s.via_alias,
+                        # whether the score cleared the head's own suggest cut.
+                        # The single min=0 fetch returns every head; the panel
+                        # shows above_threshold, the typed dropdown shows all and
+                        # annotates each match with its score.
+                        "above_threshold": s.above_threshold,
                         # operator dismissed this tag for this image — surfaced
                         # (not dropped) so the rail can show it rejected + offer
                         # one-click un-reject.
@@ -73,26 +73,6 @@ async def accept_suggestion(image_id: int):
     return jsonify({"accepted": True, "tag_id": tag_id})
 
 
-@suggestions_bp.route(
-    "/images/<int:image_id>/suggestions/alias", methods=["POST"]
-)
-async def alias_suggestion(image_id: int):
-    body = await request.get_json()
-    required = {"alias_string", "alias_category", "canonical_tag_id"}
-    if not body or not required.issubset(body):
-        return jsonify({"error": f"required: {sorted(required)}"}), 400
-    canonical_tag_id = body["canonical_tag_id"]
-    async with get_session() as session:
-        await AllowlistService(session).add_alias_and_accept(
-            image_id,
-            body["alias_string"],
-            body["alias_category"],
-            canonical_tag_id,
-        )
-        await session.commit()
-    return jsonify({"accepted": True, "tag_id": canonical_tag_id})
-
-
 @suggestions_bp.route(
     "/images/<int:image_id>/suggestions/dismiss", methods=["POST"]
 )